Liquid products produced by reaction of phosphonitrilic esters with phosphoric anhydride

ABSTRACT

NOVEL LIQUID OLIGOMERIC FLAM-RETARDANT COMPOUNDS ARE PREPARED BY HEATING TOGETHER LIQUID POLYPHOSPHONITRILIC ESTERS WITH PHOSPHORIC ANHYDRIDE.

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U Il1lI (1 Cl. 260-927 N 5 Claims AEEEDTRACT OF THE DISCLOSURE Novel liquid oligomeric flame-retardant compounds are prepared by heating together liquid polyphosphonitrilic esters with phosphoric anhydride.

This invention relates to a process for preparing viscous oligomeric flame-retardant fluids by heating together liquid phosphonitrilic esters with phosphoric anhydride.

It is desirable, for many textile purposes, to provide cellulose fibers and yarns having greatly decreased flammability. In the manufacture of rayon by the viscose method, rayon has been made permanently flame-retardant by dispersing in the rayon a flame-retardant amount of a substantially water-insoluble, liquid, phosphonitrilate polymer as disclosed by Godfrey in US. Pats. Nos. 3,455,- 713, 3,505,087 and 3,532,526 issued July 15, 1969, Apr. 7, 1970, and Oct. 6, 1970. These phosphonitrilate polymers are conventionally made by esterifying a predominately trimeric chlorophosphazene (phosphonitrilic chloride polymer). The chlorophosphazene can be made by bringing into contact elemental chlorine, phosphorus trichloride and ammonium chloride in an inert solvent at reflux temperatures as described in US. Pats. Nos. 3,359,- 080 and 3,462,247 issued Dec. 19, 1967 and Aug. 19, 1969, respectively.

Although the Godfrey compositions do not seriously degrade rayon fiber properties, it is always desirable to have more effective flame retardants allowing attainment of adequate flame retardance at a lower additive level with a consequent lowered impairment of physical prop erties of the rayon fibers and a decrease in cost. Recently, it has been discovered that phosphonitrilates of increased viscosity are improved flame retardants for rayon. Thus, it is highly desirable to provide processes for making high viscosity phosphonitrilates having enhanced flame-retardani effects in rayon.

in accordance with the present invention there is provided a process for preparing a viscous, flame-retardant fluid which comprises heating together fluid phosphonitrilic esters and phosphoric anhydride, in a ratio of about ten to twenty moles of the ester to one mole of the anhydride (phosphorus pentoxide). These flame-retardant materials are used to flame retard rayon in amounts of 1 to by weight based on the rayon.

The phosphonitrilic esters are represented by the general formula:

X M l Y/.

in which general formula n is at least 3 and X and Y represent the same or different substituents including OR groups wherein R is aliphatic, cycloaliphatic, aromatic or heterocyclic, said aliphatic radical being straight or branch chained and having 1 to 12 carbon atoms, preferably R is an alkyl or alkenyl radical having from 2 3,836,599 tented Sept. 17, 1974 to 6 carbon atoms, said cycloaliphatic radicals have 4 to 6 carbon atoms and said aromatic radicals have 6 to 10 carbon atoms; R may also have substituent groups including halogens, ether or amino groups. X and Y can also be --tSR wherein R is as previously described, thereby, providing thio-esters, which are included within the term phosphonitrilic esters. Some of the X and Y substituents can remain halogens from the phosphonitrilic halide polymer from which the ester was derived. Usually, the halogen is chlorine.

The phosphonitrilic esters (phosphonitrilates) used as reactants in the process of this invention are prepared by first making phosphonitrilic chloride polymers in a conventional process by bringing into contact elemental chlorine, phosphorus trichloride and ammonium chloride in an inert solvent at reflux temperature, the ammonium chloride being present in any time during the reaction in a proportion at least equal molar with the phosphorus trichloride. Where phosphonitrilic chloride polymers which are greatly increased in viscosity are desired, it is possible to prepare such viscous oligomeric phosphonitrilic chloride polymer having a very high proportion of phosphorus pentachloride PCl in the reaction mixture.

The phosphonitrilate polymer used in this invention is a cyclic trimer, tetramer or higher cyclic polymer, or a linear polymer and is preferably employed as a mixture of these isomers based on economy and similar perform ance to the pure compound. In any event the phos phonitrilic chloride polymers are esterified by methods well known in the art such as by reaction of the chloride with an alcohol in the presence of a tertiary amine or with a sodium alkoxide or an alkaline oxide. Where the analogs containing sulfur are desired, corresponding mercaptans and the like are used to provide the SRv radicals.

The alkyl portion of the reactant in the esterification reaction can be lower alkyl and alkylene radicals containing 1 to 6 carbon atoms such as methyl, ethyl, 2- chloroethyl, n-propyl, isopropyl, n-butyl, isobutyl, amyl, isoamyl, hexy, allyl and crotyl radicals. It is preferred that the alkyl radical be a propyl radical or that if a mixture of alkyl radicals is preferred, the mixture should average about 3 carbon atoms. In any event, it is most important that the reactant be free of active hydrogen that could influence the course of the subsequent reaction of the ester with phosphoric anhydride (P 0 Phosphoric anhydride is reacted with the phosphonitrilic ester at a temperature of about 50 to about. 180 C. for a period of at least 2 hours. The preferred reaction conditions are 2 to 12 hours at to C. Longer reaction periods such as 2436 hours may be used if this is convenient. Diluents can be added to the reaction mass; but since the phosphoric anhydride will dissolve in the liquid phosphonitrilic ester during the reaction, a solvent is not required.

The following examples further illustrate this invention. All proportions in the example and throughout the speci fication are by weight unless otherwise stated.

Example 1 A mixture of 830 gms. of n-propyl phosphonitrilicesters prepared in the usual way and containing about 65% trimer, 15% tetramer, 15 to 20% higher cyclic polymers and less than 5% linear polymers, and 61.5 gms. of phosphorus pentoxide were stirred in a nitrogen atmosphere at 146 C. for six hours. The phosphorus pentoxide dissolved within the first hour of heating. The crude reaction mixture was washed with 330 ml. of a 10% aqueous solution of NaHCO at 65 The mixture separated readily. There was obtained, after vacuum stripping of the product at 80, 1 torr 831.4 gms. of a clear iscous fluid of the following physical properties:

in a cylindrical open chamber. Controlled mixtures of oxygen and nitrogen gases are admitted into the base of the chamber and allowed to displace the normal atmos- Average molecular weight 849 (625 initially) I Viscosity tcentistokes at 25) 1100 (52 initially). Phele .When an gqmilbnum f i f m Chdm 3c] 3 I u p is obtained, the fabric samp.e is ignited with a butane Refractive index at 24 1.4639 (1.4574

. gas flame by contacting the flame to the top edge of the initially). V Ex'lm fie fabric. If the fabiic fails to ignite, the oxygen ratio of the atmosphere is increased to a level where the flame will The phosphorus-containing product of Example 1 and just propagate. Conversely, if the fabric ignites and the .i flame-retardant compound described in the Example of flame propagates, the oxygen ratio of the atmosphere is the iodfrey US. Pat. 3,455,713 were evaluated for their reduced to a level where fiame propagation is virtually flame-retardant effect in rayon yarn produced from a zero. The LOl is the minimum percentage concentration filament-forming viscose comprising 8.6 Wt. percent celof the oxygen atmosphere in which the test fabric will lulose. 6.2 wt. percent sodium hydroxide and 33.0% carignite and permit flame propagation. A control rayon. bon disulfidc, based on the weight of the cellulose, and fabric has an LOI of 18.5. having a viscosity at spinning of 6000 centipoises at 18 The vertical strip test is made by supporting a 3 by t The phosphorus-containing flame-retardant com- 10' fabric sample in a Ushaped frame which exposes pounds were injected into the viscose stream at the desired 2" by 10" fabric. The sample and frame is supported rate based on the weight of the cellulose in the viscose vertically in a draft-free chamber with the open end of and the viscose mixture passed through a high shear the fabric frame pointed down. Ignition of the fabric is blender. This provided a viscose having the flame retardmade with a Tirrell Burner fueled with butane. A 1 /2" ant dispersed therein as fine liquid particles of from 1 long flame is aligned to the base of the fabric so that to 10 microns in size. of the flame bites into the fabric. Flame contact time is Viscoscs prepared described above and containing for (a) 3 seconds and (b) 12 seconds. Data are obtained deliberately varied amounts of the phospl1oruscontain- O5 to show the length of the char and the time of after mg fiaine-retardant compounds were spun into convenflame. tional aqueous acid spin baths comprising 9.8 wt. percent Table I sets forth the results of the above described sulfuric acid, 3.0 wt. percent zine sulfate and 17.5 wt. flammability tests carried out on the fabric samples. it percent sodium sulfate at a bath temperature of 50 C. should be borne in mind that the tests were made using The yarn was wet stretched about of its original 0 knitted fabrics of relatively light construction. The verlength. Yarns having a denier of 240 and filaments tical flame-retardant test results are useful for a relative were processed by passing them through a series of baths appraisal of the fabrics tested as this test is greatly af including water wash. desulfurization, bleach, bleach fected by fabric Weight. In the vertical test, five samples acid. antichlor. and soft finish bath. The yarns were dried, are tested; the average char length must be less than 7 transferred to packages. and finally knit into circular knit inches to pass and one char of 10 inches fails the test. fabrics. The regenerated cellulose yarns prepared in this The limited oxygen test data have greater relevance manner were made up of individual filaments having fine to the flammability of normal apparel weight fabrics liquid flame-retardant particles locked in the cellulose since the limited oxygen indices are not dependent 011 matrix. fabric weight.

TABLE 1 Vertical flame test,

Percent 3 seconds 12 svetin ls FR 111 Limited Fabric vondi- Peroxygvn Char Alter Char After Flameictart'lant Sample ti()llt(l ((lll index length, llame, length, llama, (FR) No. fabric J) 10st. in. sec. in. race.

Example1 1 0.3 141 25s 10.01 13.0 10.00 1.0.

2 as isa 25.5 10.0 r 15.1 7.0 r 210N911! a 10.5 2 3-1 25.7 0.0.1 13.5 5.3 NAIF.

rboiitiut 1 t1. 0 0.08 23.8 10.0 18.0 10.0 7.0.

2 0.0 2.11 25.7 10.0 17.0 0.0 N111 5.0 3 11.0 2.30 2 1.7 10.0 17.2 0.0 N111 7.7 1 1 1.1 2.00 25.3 0.0 13.0 5.0 NM. 5 10.0 3. 20.0 3.0 NAIM 5 5.2 NAP. 0 21.0 1.30 20.3 1.0 N111 5.2 Niti 1 Over 7 inches fails in the three second test.

No after tlaine.

Nor11.]?:fail0d.

.Msays oi the flame retardant in the fabrics were made by tttlltfl'ilillllitg the phosphorus content of the neat flame retardant and the fabrics.

Table l we orth the weight amounts of flame retard- 101 in the litioncd fabric. and the weight amount it plimplmrtis in the dry regenerated cellulose fabric. the .tiruu nt t phosphorus in the dry fabric was used to calculate the amount of tlame retardant present in the conditioned fabric. The control flame retardant was that described in the Example of US. 3,455,713 and consisted of a liquid mixture of di-n-propyl phosphonitrilate polymers including about trimer, 15% tetramer, between about l5 and 20% of higher cyclic polymers and less than about 5% of linear polymers.

Flammability testing was made by employing the (1) Limited Oxygen index (LOI) method and (2) the Vertical Strip Test AATCC34-1969.

The lOl test is made by supporting a 3 x 8" conditioned fabric sample in :1 U shaped frame which mounted What is claimed is.

1.. A liquid polymeric phosphonitrilic ester produced h a process which comprises heating together at a temperature of 50 to C. for at least 2 hours (a) phosphoric anhydride with (b) a fluid phosphonitrilic ester having the general formula:

5 6 a 4. The product of claim 1 in which the reaction period FOREIGN PATENTS 18 to 36 hours- 1,452,427 8/1966 France 260-927 5. The product of claim 1 in which R is selected from the group consisting of methyl, ethyl, chloroethyl, propyl, ANTON SUTTO Primary Examiner isopropyl, butyl, isobutyl, amyl, isoamyl, hexyl, allyl and 5 crotyl radicals, U CL XR References cued 106-15 PP, 164, 168; 260-926, 988 UNITED STATES PATENTS 2,192,921 3/1940 Lipkin 260927 N 

